Subway is a form of urban public transportation, and there are two understandings of the word: it refers to the urban rail transit system that mainly runs underground, that is, "subway" or "subway" (subway; British tube, underground); In order to match the construction environment and consider the construction and operation costs, many of these systems may be converted to the ground or elevated roads outside the city center. It refers to the urban rail transit system (subway) with high density and high volume, covering all kinds of underground and above-ground road rights. Taiwan Province Province is called "MRT" and Hongkong is called "Metro".

Advantages of the subway:

Saving land: Because the value of urban land in general metropolises is high, building urban rail transit underground can save ground space and make the ground land available for other uses.

Noise reduction: the urban rail is built underground, which can reduce the noise on the ground.

Reduce interference: Because the running route of the subway does not overlap or cross other traffic systems (such as ground roads), there is less traffic interference, which can save a lot of commuting time.

Energy saving: Under the problem of global warming, subway is the best public transport. Because the subway runs smoothly, it saves a lot of commuting time, makes people happy, and also replaces a lot of energy consumed by driving.

Reduce pollution: ordinary cars use gasoline or petroleum as energy, and subways use electric energy, so there is no tail gas emission and no pollution to the environment.